Medical diagnostic radiation imaging systems employing multiple modes of image acquisition are well known in the art. Such systems employ a source of penetrative radiation, such as x-rays, for propagating the radiation along a predetermined path. An image intensifier tube is interposed in the radiation path, and spaced from the source so that a patient or subject can be placed between the source and tube. The intensifier tube has an input face, and apparatus and circuitry for producing at a smaller output face, a visible image of a pattern of penetrative radiation incident on the input face.
Apparatus and circuitry is provided for producing images of the input radiation pattern in a variety of ways. One such apparatus is a spot film device, which includes means for supporting a piece of phosphor screen and light sensitive film between the patient and the input face of the intensifier tube. When an exposure is made, the pattern of x-rays emergent from the patient exposes the film, and some of the energy passes along to the input face of the intensifier tube which substantially simultaneously produces a visible image, at its output face, of the radiation pattern which also exposed the film.
Downstream from the output face of the image tube is a well known device, often called an "optical cube", which divides light energy from the visible light image into several components, each component, in some versions of equipment, directed along its own separate path, exiting the optical cube through one or more selectable "ports." Viewing one of these ports is a spot film camera, which is a camera containing film sensitive to the visible light, for making a film record of the image appearing at the output face of the image tube. Viewing another port is interposed a cine camera which includes means for exposing light sensitive motion picture film to make, over a period of time, a "movie" of the image at the image tube output.
The forms of image acquisition apparatus associated with operation of the spot film device, the spot film camera, and the cine camera result in the acquisition of an image in analog form, i.e., on film. Differing radiation intensities and exposure times are used in acquiring these film images. Such analogically acquired film images are not viewable in real time. Accordingly, a technician or radiologist operating the system in such a mode has, without other provision, no way of knowing immediately whether the exposure from which the image was acquired was appropriate in intensity and exposure time to cause the acquisition of a good analog image.
Viewing still another port is interposed a television camera for receiving a continuous light image of the image tube output. The television camera includes circuitry for scanning a target at a predetermined one of several scan rates, and for producing a video signal defining the brightness pattern of the viewed image tube output image, and also for producing appropriate synchronization signals which, along with the video signal, form an ensemble for producing on a video monitor a television image of the viewed output, in a scan format determined by the synchronization signals.
The video signal is also directed to a complex component known as a "digital acquisition system". The digital acquisition system includes means for digitizing the video, and subsequently storing and operating upon the digital data, in order to produce, at another monitor, an enhanced visible image corresponding to the stored digital data.
The television system also includes apparatus and circuitry for defining an adjustable set of television camera operating parameters, such as iris opening, scan rate, scan mode (interlaced or sequential) AGC, video gain, bias light, line lock, filter mode, and gamma.
The television camera in the system has three general uses. First, in digital image acquisition operating modes, the television camera provides the analog video signal to be digitized, stored and processed by the digital acquisition system. Secondly, the television camera, in a fluoroscopic mode, is used to produce at its associated monitor a continuous (real time) television picture of the image tube output, a particular form of analog image acquisition. Thirdly, the television camera can be used in what is known as "analog verification" mode. In analog verification mode, the image produced by the television camera at its monitor is not intended as the prime image to be studied. Rather, the television camera in this analog verification mode is used to produce a real time image. This image is useful in verifying that a proper radiation exposure, or series of exposures, has taken place, where the prime mode is the acquisition of an analog image by means of a device e.g., spot film device, spot film camera, cine camera, which is not itself capable of producing a real time image. The non-real time image consequently cannot be viewed without the aid of the instantaneously operable television chain.
Examples of prior art multimode radiation imaging camera systems similar to that described above are: Models Beta IIIA and Beta IV, manufactured by Picker International of Cleveland, Ohio, U.S.A.; Model 4112, manufactured by ADAC Inc., of San Jose, California, U.S.A.
Prior art systems have included digital storage means associated with the digital acquisition system for storing sets of representations of television camera operating parameters. The storage has been by means of software programs.
The digital acquisition system is capable of digital operation in a number of modes. In response to the selection of a digital mode of operation, the stored program controls the television camera to establish a particular set of operating parameters for the camera which are deemed appropriate for the particular digital mode selected.
This means of camera control, however, has no connection with analog image acquisition operation modes. As mentioned above, different analog image acquisition modes incorporate differing intensities and durations of x-ray exposure. Prior art television cameras have no facility for adjusting camera operating parameters to tailor the camera response optimally to the intensity and duration of exposure utilized in acquiring images in the various analog acquisition prime study modes. As a result, the television images generated in connection with operation of the television camera for analog verification are not explicitly tailored for each analog acquisition prime mode. Rather, the camera parameters have been set at fixed values which are deemed to be the best compromise for all the analog modes. Consequently, the analog verification images produced by the television camera at its associated monitor have been less than optimal in their characteristics, rendering more difficult and uncertain the important function of analog verification itself.
For example, sometimes the image is excessively faint, and at other times it is excessively bright and/or "contrasty". Sometimes, the compromise-selected scan rate employed by the television camera is too slow to produce a pleasing and useful image for verification.
Regarding the prior art adjustment of camera parameters in the digital mode, it sometimes is advantageous to alter the camera parameters which are stored in the software program and which are used to accommodate the camera to various digital procedures. This condition can result, sometimes from variations among different patients, or variations in the nature of the study performed. The prior art system is capable of alteration of these stored parameters only by reprogramming the digital acquisition system. This entails the services of a computer technician, and sometimes results in the need to remove the camera and the data storage means entirely to a remote service center for reprogramming. Also, this condition inhibits flexibility in being able to "fine tune" the system on the site by the actual technician or radiologist using the system.
As mentioned above, one of the parameters adjusted in the television camera operation is the scan rate. In some studies, the scan rate can be quite slow. In such instances, when the scan rate is slow, the image produced at the television camera monitor can become rather unpleasant to view, due to excessive "flicker" and/or long periods of darkness on the screen between successive images. Also, images acquired at slow scan rates are not particularly useful for any purpose.
It is an object of this invention to provide means for control of a television camera in a multi-mode radiation imaging system to tailor the camera response optimally for analog verification of each of a number of prime analog study modes, as well as to provide on site flexibility in adjustment of stored representations of camera operating parameter decisions for application to the camera in response to a selection of a predetermined operating mode, and to compensate system operation for slow scan rates when used.